Low Power Tissue Sealing Device and Method

ABSTRACT

A surgical system and associated method for fusing tissue are disclosed. The system has an electrosurgical generator capable of delivering electrosurgical power, a surgical instrument, and a power control circuit. The surgical instrument is electrically connected to the electrosurgical generator and adapted to transfer electrosurgical power from the electrosurgical generator to a distal end of the surgical instrument. The power control circuit controls the delivery of radio frequency energy to tissue in contact with the distal end of the surgical instrument. The surgical system is configured to deliver radio frequency energy at a non-pulsing power to the tissue for a period of time of 3 seconds or less. The non-pulsing power has no less than 7 Watts and no more than 35 Watts, and further causes the tissue to begin to desiccate and to fuse within the period of time.

PRIORITY AND RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/153,513 filed on Jun. 6, 2011 and entitled “LOW POWER TISSUE SEALINGDEVICE AND METHOD,” which claims the benefit of Provisional U.S.Application No. 61/352,114 filed on Jun. 7, 2010, the entire disclosuresof which are hereby incorporated by reference into the presentapplication in its entirety and for all proper purposes.

FIELD OF THE INVENTION

Aspects of the present invention relate to electrosurgical procedures,techniques, and devices that utilize radiofrequency energy to seal bloodvessels during surgical procedures. In particular, and by no means oflimitation, aspects of the present invention relate to devices andtechniques for sealing precisely placed or otherwise sensitive ordifficult to access blood vessels often found in micro-surgicalprocedures, difficult to access anatomy or general surgery in pediatricpatients.

BACKGROUND

The use of electrosurgical energy in vessel sealing surgical proceduresis common and has been used in conjunction with a variety of surgicaltechniques for many years. In general, electrosurgical devices used invessel sealing rely on a combination of pressure and high frequencyelectric energy applied to biological tissue as a way to cut, coagulate,desiccate or seal tissue, for example, blood vessels. In the case ofvessel sealing, the electrosurgical energy acts to create collagenmelting and tissue fusion. Most RF surgical devices on the market todayand described in the prior art have power delivery systems and endeffectors that are sized to accommodate a wide range of situations,tissue thicknesses, tissue volume, and end effector bite sizes. Inparticular, vessel sealing technology has always relied upon the use ofrelatively high current settings and large end effector sizes to createa seal in varying surgical situations. No one has been able to produce areliable vessel sealing instrument that operates at currents below 2Amps.

For coagulation or blood vessel sealing with known devices, the averagepower density delivered by the end effector is typically reduced belowthe threshold of cutting. In some cases (e.g. a monopolar coagulationinstrument) a modulated sine wave is used with the overall effect beinga slower heating process which causes tissue to coagulate rather thanburn and/or char to the point of cutting. In some simple dual functioncoagulation/cutting devices, a lower duty cycle is used for acoagulation mode and a higher duty cycle is used for a cutting mode withthe same equipment. Coagulation and in particular vessel sealingtechniques present unique challenges in electrosurgery

While some modern electrosurgical generators provide modulated waveformswith power adjusted in real time based on changes of the tissuecharacteristics (e.g. impedance), none have been able to address thecomplexities and sensitivities that arise when dealing with bloodvessels located in delicate surgical sites or other difficult to reachblood vessels. None of the prior art or products currently offeredcombine aspects of applied pressure, low-power energy delivery, waveformmodulation, and instrument size/configuration to safely and effectivelyseal the blood vessels that are often presented in micro-surgicalprocedures, difficult to access anatomy or pediatric general surgery.

Recent advances in vessel sealing technology have specifically abandonedan attempt to address this specialized market and instead focus onlarger devices and techniques for sealing larger vessels more commonlyfound in general surgery or on “one-size-fits all” devices. U.S. Pat.No. 5,827,271 describes how earlier attempts to seal vessels withelectrosurgery were unsuccessful in part because they attempted to applyrelatively low currents to the vessels. As a solution, the advancesdescribed in U.S. Pat. No. 5,827,271 relate to increasing the currentapplied to the blood vessel above a certain threshold. The prior art inthis field is consistent in its recognition that a high current and highgenerator power output is required to seal vessels. None of the priorart addresses the unique circumstances presented with small caliberblood vessels that present during micro-surgical procedures, difficultto access anatomy or general surgery in pediatric patients. None of theart accounts for a technique or device that effectively and safely sealsblood vessels with an instrument that is smaller in size (both in theshaft and entry point features) and configured to be more effectivewhich working in smaller spaces and with smaller vessel calibers. Noneof the prior art recognizes the role of the surgical instrument size andend effector surface area in the development of effective vessel sealingtechniques and energy delivery sequencing.

SUMMARY OF THE INVENTION

In accordance with one aspect, an exemplary surgical system has anelectrosurgical generator capable of delivering electrosurgical power, asurgical instrument, and a power control circuit. The surgicalinstrument is electrically connected to the electrosurgical generatorand adapted to transfer electrosurgical power from the electrosurgicalgenerator to a distal end of the surgical instrument. The power controlcircuit controls the delivery of radio frequency energy to tissue incontact with the distal end of the surgical instrument. The surgicalsystem is configured to deliver radio frequency energy at a non-pulsingpower to the tissue for a period of time of 3 seconds or less. Thenon-pulsing power has no less than 7 Watts and no more than 35 Watts,and further causes the tissue to begin to desiccate and to fuse withinthe period of time.

According to another aspect, an exemplary power control system fordelivering radio frequency energy to a surgical instrument is provided.The power control system has a power supply for delivering an outputvoltage and an output current to a distal end of the surgicalinstrument, a sensing circuit, and a power sequencing module. Thesensing circuit detects parameters indicative of an impedance of atissue portion being fused. The power sequencing module automaticallysequences an electrosurgical power delivered to the surgical instrument.The power sequencing module is adapted to apply non-pulsing power of noless than 7 Watts and no more than 35 Watts to the tissue portion for aperiod of time of 3 seconds or less. The period of time is measured fromthe beginning of the application of the non-pulsing power and continuesthrough the beginning of a desiccation of the tissue portion and througha drying out and the fusing of the tissue portion.

According to another aspect, an exemplary surgical system for fusingtissue is provided. The system has an electrosurgical generator capableof delivering electrosurgical power, a surgical instrument, and a powercontrol circuit. The surgical instrument is electrically connected tothe electro surgical generator and adapted to transfer electrosurgicalpower from the electrosurgical generator to a distal end of the surgicalinstrument. The power control circuit controls the delivery of radiofrequency energy to the tissue through the distal end of the surgicalinstrument. The surgical system is configured to deliver a radiofrequency energy to the tissue, the radio frequency energy having anon-pulsed power having an output current and an output voltage. Thesurgical system is further configured to apply the non-pulsed power tothe tissue for a period of time while the non-pulsed power is held atbetween 7 Watts and 35 Watts, while allowing the output current and theoutput voltage to fluctuate. The period of time is measured from thebeginning of the application of the non-pulsed power and continuesthrough fusing of the tissue. The non-pulsed power causes the tissue tobegin to desiccate within the period of time. The period of time is 3seconds or less.

According to another aspect, an exemplary method of fusing tissue isprovided. The method includes providing a surgical system having anelectrosurgical generator and a surgical instrument surgical instrumentelectrically connected to the electrosurgical generator and adapted totransfer electrosurgical power from the electrosurgical generator to adistal end of the surgical instrument. The method further includesdelivering a radio frequency energy to the tissue, the radio frequencyenergy having a non-pulsed power having an output current and an outputvoltage. The method further includes applying the non-pulsed power tothe tissue for a period of time while the non-pulsed power is held atbetween 7 Watts and 35 Watts, while allowing the output current and theoutput voltage to fluctuate. The period of time is measured from thebeginning of the application of the non-pulsed power and continuesthrough fusing of the tissue, and the non-pulsed power causes the tissueto begin to desiccate within the period of time, wherein the period oftime is 3 seconds or less.

Other aspects will become apparent to one of skill in the art upon areview of the following drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects, objects and advantages, and a more completeunderstanding of the present invention are apparent and more readilyappreciated by reference to the following Detailed Description and tothe appended claims when taken in conjunction with the accompanyingDrawings, wherein:

FIG. 1 is a side view of an electrosurgical instrument in accordancewith aspects of the present invention;

FIG. 2 is a perspective view of the electrosurgical instrument in FIG.1;

FIGS. 3A-3B are various views of an end effector constructed inaccordance with aspects of the present invention;

FIG. 4 is a close up of the mechanical and electrical engagementmechanisms of the electrosurgical instrument shown in FIG. 1;

FIG. 5 is an exploded perspective view of the mechanisms shown in FIG.4;

FIGS. 6A-6E show several views of an electrical cable and associatedconnection devices in accordance with aspects of the present invention;

FIG. 7 is a block diagram of an RF power generator system in accordancewith aspects of the present invention;

FIG. 8 is a prior art vessel sealing impedance curve;

FIG. 9 is an end effector constructed in accordance with aspects of thepresent invention; and

FIGS. 10-14 are oscilloscope traces of various vessel sealing proceduresin accordance with aspects of the present invention.

Other aspects of devices and methods in accordance with the presentinvention will become known to those of skill in the art when read inconjunction with the following disclosure.

DETAILED DESCRIPTION

Throughout this specification references are made to the use of variousmaterials, combinations, mechanical configurations, ranges and otheraspects that may be used in various combinations to form one or moredevices and methods in accordance with aspects of the present invention.It should be understood, both to one of skill in the art as well as theexamining divisions in the United States Patent Office and PatentOffices throughout the world, that each of the lists of materials,examples, and other embodiments are included herein in order to teachone of skill in the art that they may be combined into variousalternative embodiments, without requiring specific claim permutationsof these individual features, and without departing from the spirit andscope of the invention. The claims as presented herein, as well as anypotential future amendments to those claims, may include one or morecombinations of these materials, ranges and other alternatives withoutdeparting from the spirit and scope of the invention described herein.In particular it is contemplated that one of skill in the art wouldrecognize and find adequate support in the written description for anycombination of the features disclosed herein, whether described in asingle example or embodiment, or described in multiple and disjointedsections of the written description. The description of these variousexample and options is specifically drafted to comply with 35 U.S.C.§112 of the United States Patent Laws, Article 123(2) of the EuropeanPatent Laws as well as other similar national country laws relating tothe adequacy of the written description.

Aspects of a device constructed in accordance with the present inventiongenerally pertain to a low-power vessel sealing system. Application ofsuch devices have particular applicability in pediatric surgery andother situations where small caliber blood vessels may be encounteredsuch as micro-surgery, difficult to access anatomy and all aspects ofpediatric surgery. In addition, devices constructed in accordance withaspects of the present invention allow smaller profile instruments whichin turn allow smaller incisions to be made during the associatedsurgical procedure. A system constructed in accordance with aspects ofthe present invention has as its major components an RF generator and abipolar grasper/dissector/sealer instrument hand piece that plugs intothe generator. Various power sequencing and control systems areincorporated into the generator and system logic that enable effectiveand safe vessel sealing capabilities at lower power outputs than iscurrently available or otherwise known in the art.

Features of an instrument and vessel sealing system constructed inaccordance with aspects of the present invention may include one or moreof the following, each of which is described in greater detail below.

Orientation and Operation of End Effectors

Aspects of a device constructed in accordance with the present inventioninclude opposing electrically isolated end effector jaw members thatprovide energy delivery to tissue, such as a blood vessel, undergoing asurgical procedure. The jaws preferably open in a simultaneous dualaction fashion, although other jaw movement dynamics are contemplated.The jaws are located on the distal end of a shaft that serves tomaximize surgical site visibility in either open, endoscopic orlaparoscopic procedures. The length of the instrument shaft may varyfrom 10 cm to 30 cm depending on the designed use. In one embodiment theinstrument shaft may vary from 15 cm to 20 cm long. Furthermore, aspectsof the present invention can be used in connection with both rigid shaftinstruments and flexible shaft instruments such as might be found insteerable surgical systems or robotic surgical systems.

The size of the jaws may range from 1.0-3.5 mm in width and from8.0-12.0 mm in length. The surfaces of the jaws may include one or morenon-conductive elements that function to maintain electrical isolationbetween the jaw surfaces and keep the electrodes from shorting out.Preferably the jaws are designed to close in a parallel fashion, i.e.both jaw surfaces move in coordination with each other upon activationby a user. The instrument or end effector itself may or may not be builtwith a cutting instrument that serves to divide the tissue after sealingis accomplished.

In accordance with one aspect, an instrument end effector constructed inaccordance with the present invention applies pressure to the tissue tobe sealed in the range of 75-110 psi so that the tissue is adequatelycompressed prior to the sealing action taking place.

There is preferably limited play in the motion of the instrument handle.In one embodiment the ring handle design enables a close to 1-1 openingand closing of the jaws. A ratchet point may be incorporated into thehandle assembly so that full jaw closure and the required pressure isapplied prior to the sealing function.

Generator Capabilities and Function

With respect to the generator and electrical aspects of the presentinvention, features of a device constructed in accordance with aspectsof the present invention include one or more of the following, each ofwhich is described in greater detail below.

Energy is preferably applied to the tissue undergoing a surgicalprocedure at a constant power. The power delivery cycle may terminatewhen one or more of the following occurs: a) voltage reaches a maximumlevel not to exceed a set level such as 80 Volts RMS or 100 Volts RMS;b) impedance reaches a final value of between 180-350 ohms; and c) amaximum seal time of between 2 and 5 seconds is reached. In addition,voltage or current limits may be put in place that further confine theoperational parameters of the power delivery system.

The generator has a power capability in the range of 25-35 Watts totalpower, but typical operation is preferably in the range of 8-15 Watts inorder to control resolution and accuracy of the power output and tominimize the possibility of tissue charring and other damaging effects.A voltage limit incorporated into the generator operation minimizes thepotential for tissue damage during a sealing procedure.

Maximum current delivery is under 2 Amps, and typical operation is inthe range of 0.75-1.5 Amps. Maximum voltage of the system is 100 VoltsRMS. The typical maximum voltage is in the range of 70-85 Volts RMS.

The above summary should be considered as one set of overall designparameters and not as any type of exclusive requirements for how asystem or particular instrument is required to be designed in accordancewith aspects of the present invention. In addition, any examples giventhroughout this specification, and any data or test results giventhroughout this specification, should not be used as evidence duringprosecution of the claims herein of any intention by the applicant tolimit the scope of any claims to those particular embodiments orexamples. For example, maximum current delivery may be limited to under1.5 Amps in one embodiment, under 1.0 amps in another embodiment andunder 0.5 amps in yet another embodiment. In addition to the above,operation of the system may be in the range of 1.0-1.25 Amps. In anotherembodiment operation of the system may be in the range of 0.5 to 2 Amps.In other embodiments, maximum voltage of the system is 75 Volts RMS. Inyet other embodiments maximum voltage of the system is 50 Volts RMS. Inanother embodiment the typical maximum voltage is in the range of 50-100Volts RMS.

One of skill in the art would know to utilize various permutations ofthe described examples to arrive at the claim scope submitted below.

With reference to FIGS. 1-6, various drawings are shown that depict oneexample of a surgical instrument 100 that may be used in connection withaspects of the present invention. As shown in FIGS. 1-6, surgicalinstrument 100 is depicted as a forceps for use with a variety oflaparoscopic and open procedures. As such, instrument 100 includes anelongated shaft 102 with an end effector 104 located at a distal end ofthe shaft 102. The shaft 102 and end effector 104 are coupled with arotational element 114 that allows a user to rotate the shaft 102 andend effector 104 about the longitudinal axis of the shaft 102 therebyenabling various presentations of the end effector 104 within a surgicalsite.

A handle assembly 106 generally includes a stationary handle portion 108and a thumb lever portion 110 that operate in conjunction with anactuation mechanism 119 to control the movement, physical engagement ofand electrical engagement of the end effector 104. Each of the handleportion 108 and thumb lever portion 110 define an area for a user'sfingers to engage the instrument and operate the handle assembly 106 ina scissor-like movement. As such, movement of the thumb lever portion110 with respect to the handle portion 108 facilitates movement of theend effector from an open position to a closed position. In oneembodiment the handle portion 108 and the thumb level portion 110 enablea single action movement of the end effector 104. A ratchet mechanism112 is included for selectively locking the handle assembly 106 at aselected position during movement. In another embodiment, severalratchet stops are include so that a user can select a closure positionand/or pressure applied by the end effector around a tissue sample.Electrical cable assembly 116 extends from a position in anelectro-mechanical sub-assembly 118 and serves generally to connect thesurgical instrument 100 to a power source, such as a radio frequencygenerator described below. Further details of the electrical cableassembly 116 are described below. FIG. 2 shows the surgical instrument100 in a perspective view but generally illustrates the same features asthose described in conjunction with FIG. 1 and that description is notrepeated here.

FIGS. 3A-3B show details of the end effector 104 of the surgicalinstrument 100. With continuing reference to FIGS. 3A-3B, the endeffector 104 is shown in various perspectives and with varying detail.In the example of FIGS. 3A-3B, the end effector 104 is shown as agrasper/dissector, sealer combination. However, it is contemplated thatvarious other instrument configurations may be employed withoutdeparting from the spirit and scope of the invention. For example,various alternate configurations of the grasper itself may be employedas well as different instruments, such as a dissector or cutter may beused in connection with the sealing aspects disclosed herein. The sizeand overall shape of the end effector may also be varied in accordancewith other aspects of a device constructed in accordance with aspects ofthe present invention.

With respect to the grasper/dissector, sealer end effector 104 depictedin FIGS. 3A-3C, the end effector 104 includes opposing grasper portions130 and 132 that are adapted to open and close as a result of the actionof the handle assembly 108. Cables 122 and 124 engage with each of thegrasper portions 130 and 132 and extend through the shaft 102 back tothe handle assembly 108 where they engage with an electrical connectionand linkage system 118. A tension block 126 secures the cables 122 and124 at the distal end of the shaft 102 and provide a mechanism to coupleeach of the cables 122 and 124 with the grasper portions 130 and 132. Incombination, this mechanical arrangement allows the grasper portions 130and 132 to open and close when the thumb lever portion 110 is engaged bya user. As shown, the embodiment of the grasper/sealer 100 provides forboth grasper portions 130 and 132 to move simultaneously in a singleaction motion when actuated by thumb lever portion 110.

With reference to FIGS. 4-6E, details of the electrical connection andlinkage system 118 are shown. Overall, the electrical connection andlinkage system 118 provides both a mechanical interface between thehandle assembly 106 and the effected movement of the grasper portions130 and 132, as well as an electrical interface between the cableassembly 116, which is connected to an electrosurgical power source, andthe grasper portions 130 and 132. Actuation cables 151 a and 151 bextend from the jaw portions 130 and 132, are routed to the handleassembly 106 and are crimped and constrained to the cable collar 150.Electrical connections are made to the proximal ends of the actuationcables 151 a and 151 b. In some embodiments, the actuation cables 151 aand 151 b also conduct the current to the end effector 104 and to thetissue undergoing a procedure.

Actuation cables 151 a and 151 b route through the cable collar 150.Joined to each cable is a mechanically fastened ferrule crimp 200 a and200 b near the proximal end of both cables, which allows the actuationcables to be pulled (to clamp/close the jaw portions 130 and 132) andpushed (to open the jaw portions 130 and 132). In the short section ofactuation cables proximal to the ferrule crimp (shown as 151 a), each ofthe two cables are electrically connected to the two poles of theelectrosurgical power wires (182 and 184). This connection can be donewith an additional electrical ferrule (crimped) or soldered. This is nota load bearing connection; simply electrical. The electrosurgical powerwires wrap around the cable collar 150 to provide enough path length toallow the cable collar to rotate approximately one full rotation withoutcausing undue strain on the power wires or electrical connections. Thetwo poles of the electrosurgical trigger switch (188 and 186) form aclosed loop in the flex circuit 142 (See FIG. 6B) when the dome contactis depressed by the trigger 152. The dome switch circuit activates theelectrosurgical connection to actuation cables 151 a and 151 b, therebyconducting current down the length of the shaft to grasper portions 130and 132. The rest state is an open loop when the trigger 152 is notdepressed and there is no electrosurgical connection.

In accordance with proper functioning of the instrument and system isthat the two poles remain electrically isolated at all times. Powerwires 182 and 184, solder/crimp connections 182 a and 182 b (not shown),151 a and 151 b, and jaw portions 130 and 132 have to remain isolatedfrom each other. FIG. 6D shows how along the length of the Shaft 102 theactuation cables are isolated by an extrusion 210, and encapsulated onthe outside by electrically isolating heat-shrink jacket 212.

FIG. 6C and 6E shows how actuator cables 151 a and 151 b are separatedby insulator 220, and how jaw portions 130 and 132 are separated byinsulator 222. Extrusion 210 and insulator 220 (with jacket 212enclosing the tracks on the outside) guide the actuator cables to allowthem to be pushed as well as pulled. The constrained track allows theassembly to push a flexible cable in order to open the jaw portions 130and 132

Located on an interior surface of grasper portion 130 are a series ofnon-conductive raised elements 134 a, 134 b, and 134 c that ensure thatthe interior conductive surfaces of grasper portions 130 and 132 do notphysically touch and are maintained at a constant and predictableseparation distance from each other when the grasper portions 130 and132 are in a closed position. Raised elements 134 a, 134 b and 134 c maybe on either of the interior surfaces of grasper portions 130 or 132.

In other embodiments, non-conductive elements 134 a, 134 b and 134 c maybe made of a variety of non-conductive material. For example thenon-conductive elements may be made of a ceramic material, nylon,polystryenes, Nylons, Syndiotacticpolystryrene (SPS), PolybutyleneTerephthalate (PBT), Polycarbonate (PC), Acrylonitrile Butadiene Styrene(ABS), Polyphthalamide (PPA), Polymide, Polyethylene Terephthalate(PET), Polyamide-imide (PAl), Acrylic (PMMA), Polystyrene (PS and HIPS),Polyether Sulfone (PES), Aliphatic Polyketone, Acetal (POM) Copolymer,Polyurethane (PU and TPU), Nylon with Polyphenylene-oxide dispersion andAcrylonitrile Styrene Acrylate.

Handle portion 108 includes an exterior shell portion 144 that formspart of a casing that surrounds several of the components withinelectrical connection and linkage system 118. A second portion of thecasing is indicated as reference number 146. Casing portion 146 connectsto thumb lever 110. Enclosed in a top portion of casing portion 146 area shaft collar 148, a cable collar 150, and a ring cable collar 154 thatserve to actively engage the shaft assembly 102 with the overall handleassembly 118. Cable assembly 116 is coupled with a flex circuit 142. Alength of cable 140 extends from the cable assembly 116 and is coiledabout cable collar 150 in order to allow the shaft assembly 102 torotate freely without undue resistance to the user. Rotational element114 couples to the housing portions 144 and 146 and allow a user torotate the shaft assembly 102 and alter the presentation of the endeffector 104 during a procedure.

Various fastening devices secure the components of the handle assemblytogether such as screws 158, 160, 162, and 164 as well as pin 156.Alternatively, sonic welding or other connection techniques may beutilized to secure the components together. Switch 152 engages with thethumb lever 110 and is adapted to engage the power delivery throughcable assembly 116 as delivered from an electrosurgical generator.

FIGS. 6A-6C show the components that form the electrical connectionbetween a power source, such as a radio frequency electro surgicalgenerator, and the device 100, eventually delivering the electrosurgicalenergy to the end effector 104. The connector 170 is keyed for insertioninto the output of an electrosurgical generator (See e.g. FIG. 7). Theconnector 170 is coupled to the cable assembly 116. The length of thecable assembly 116 is determined by the particular application but ispreferably long enough to allow operation of the instrument at aposition remote from the electrosurgical generator. At an end of thecable assembly 116 opposite the connector 170, a strain relief device180 is intermediate with an exit portion 190 of the cable assembly 116.

The cable assembly 116 houses four conductors, 182, 184, 186, and 188.In general the four conductors provide the RF power 182 and 184 to theend effector 104 a common/ground conductor 186 and a switch conductor188 that couples with an identification resistor that signals thegeneral as to what type of device is plugged in to the power source.

With reference to FIG. 7, a schematic of an RF generator 300 is shown.The use of an RF generator in connection with the delivery ofelectrosurgical energy is generally known in the art. However, aspectsdescribed herein that relate to the functioning and sequencing oflow-power and energy delivery has not been described before.

Generator 300 inputs AC power from a wall outlet 302 and delivers thatAC power to a power module 304 such as an IEC power entry module. Powermodule 304 may include such components as a DPDT switch 306 and 2replaceable fuses 308. Power is transferred from power module 304 to apower supply unit 310. Preferably in connection with medicalapplications the power supply unit 310 is a medical grade power supplysuch as a CSS65-24 from Lambda. DC to DC converters 312 and 314 converta 24 volt output of the power supply 310 into a pair of 12 volt outputsthat are used to power control circuits. Power supply 310 then serves asthe inputs 320 and 330 to a Buck-Boost Converter 340. The output of theconverter 340 is passed to an H-Bridge circuit 345 which then passesthat signal to a resonant LC transformer circuit 350. The transformercircuit 350 includes capacitor 352, inductor 354 and transformer 356. Inone embodiment, transformer 356 is a 1:9 transformer. From thetransformer 356, power is delivered to a load 400. In one embodiment,load 400 is a grasper/sealer instrument 100 as described above inconnection with FIGS. 1-6 and the power delivered to instrument 100 isno more than 25 Watts, no more than 80 Volts RMS, and less than 2 AmpsRMS.

Controller 360, in conjunction with the components described below, isused to sense various aspects of the energy applied to load 400, andadjust one or more of the energy characteristics in response to thevessel sealing process. Coupled to the load 400 (e.g. an electrosurgicalinstrument) are a current sensor circuit 390 and a voltage sensorcircuit 395. Based on the sensed current and voltage, op-amps 392 and394 pass these values to conversion circuits 380 that includes voltageRMS—DC Converter 382 and a current RMS—DC Converter 384. A multiplier386 and a divider 388 derive power and impedance respectively from thesensed voltage and current. Each of the circuits 382, 384, 386 and 388provide input data to the controller 360 which can then process andanalyze the various input to indicate the state of the vessel sealingprocess. These circuits 382, 384, 386 and 388 also may be used as directfeedback signals to the Buck-Boost converter controller.

In some embodiment a user input panel 368 may be included that allowsoperator interaction with the controller and may include a display andsome form of input device (such as a keyboard, mouse, pointer, dials orbuttons). Data from the controller 360 may be output via analog ordigital means such as an RS-232 connector 362, programming port 364 ormemory chip 366.

FIG. 8, shows a known impedance curve as applied to RF vessel sealingand shows the changing impedance of a vessel and the various phases thevessel impedance goes through during an RF electrosurgical sealingprocess. In FIG. 8, the impedance is responding to changes in the powerapplied to the jaws of the surgical device. The tissue being sealed goesthrough several stages of change in order to achieve a complete seal.Prior systems effected vessel sealing by adjusting the power through thesealing cycle by pulsing the current and voltage applied to the tissueaccording to observing the rate of change of impedance during the risingsection of the curve from the minimum value through the denaturation anddesiccation and adjusting the power to the vessel in order to controlthat change. However, these systems cannot apply a uniform powerdelivery scheme that would apply to vessels of varying sizes.

Power Delivery Sequencing

Throughout the sealing process, the impedance of the vessel iscalculated in real-time by measuring the voltage and current to thejaws. (Z=V/I). Since it is known that the impedance will follow theprescribed format, impedance thresholds can be set which act as trippoints to cause the power profile curve to advance to the next phase ofits settings. However, if the impedance limit is not met before the timehas elapsed, the curve advances to the next phase. Each phase of thecurve advances to the next phase according to an “OR” logic. If any oneof the parameters is met according to impedance or time, the powerprofile is advanced.

In accordance with one aspect of the present invention it is desirableto achieve a single set of parameters that would be effective at sealingblood vessels with a diameter under 6 mm, typical in micro-surgeryapplications, pediatric patients, and surgical sites that are oftendifficult to reach and/or visualize.

EXAMPLES

The following examples are illustrative of aspects of the presentinvention but are not meant to be limiting under 35 U.S.C. §112 of theUnited States Patent Laws, Article 123(2) of the European Patent Laws orany corresponding national country patent laws concerning the adequacyof the written description. By giving these examples, it is submittedthat variations in the scope of the test results and correspondingimplementations and claim scope are clearly and unambiguously disclosedto one of skill in the art.

Vessel Sealing Results

Table 1 shows the electrical characteristics associated with variousseals performed according to aspects of the present invention.

TABLE 1 Vessel Peak Peak Seal Burst Seal Size Power Current Voltage timePressure Number (mm) (W) (A) (Vrms) (sec) (mm Hg) 41-3 5 10 80 1.3 68741-4 5 10 78 1.5 687 41-5 4 10 1.1 84 1.1 1034+ 41-6 4 10 0.9 80 1.11034+ 42-3 3.5 10 0.8 81 1.6 899 42-4 3.5 8 1.05 82 1.4 899 43-1 5 8 180 2.3 786 43-2 5 10 0.95 82 2.2 786 43-3 5 15 1 80 2.2 889 43-4 5 10 183 2.6 889 43-5 5 15 1 83 2.5 682 43-6 5 10 1 76 2.1 682 44-1 1.5 15 180 1.5 1034+ 44-2 1.5 15 1 84 0.8 1034+ 44-3 3 10 1 81 1.1 889 44-4 3 101.15 78 2.1 424 45-3 2 8 78 1.5 584 45-4 2 15 82 1.5 584 45-5 4 10 2 73445-6 4 10 1.19 81 2.4 734 46-1 5 15 78 1.25 780 46-2 5 15 80 1.25 78046-5 3.5 15 78 3.5 682 46-6 3.5 15 78 1.25 682 47-1 5 15 0.82 38 3 69847-2 5 15 0.84 34 3 698 47-3 2.5 15 81 1.5 589 47-4 2 15 77 0.8 589 47-54.5 15 0.94 42 1.7 1034+ 47-6 4.5 15 78 1.7 1034+ 48-1 2.5 10 0.9 80 0.5424 48-2 2.5 10 1 80 1.2 424 48-3 3 10 77 1.3 693 48-4 3 10 1.15 82 1.1693 49-3 4 10 0.8 81 0.4 801 49-4 4 10 0.78 84 0.35 801 49-5 6 10 0.8481 3 526 49-6 6 10 0.86 82 2.1 526 50-1 6 15 0.82 82 1.8 729 50-2 6 150.84 80 1.95 729 50-3 4 15 0.76 81 0.6 536 50-4 4 15 0.8 82 0.7 536 50-53 15 0.78 81 0.6 623 50-6 3 15 0.84 84 0.85 623 51-1 6 15 708 51-2 6 150.72 79 1.3 708 51-3 3 15 0.86 82 1.2 1034+ 51-4 3 15 0.84 81 0.8 1034+51-5 2 15 478 51-6 2 15 0.8 82 0.55 478 52-3 3 10 0.8 1.25 1034+ 52-4 310 0.78 81 0.4 1034+ 52-5 2 15 0.88 80 0.85 532 52-6 2 10 0.92 81 0.9532

With respect to the test results described in Table 1, the examples werecompleted by the power being held constant while current and voltagewere allowed to float to the maximum values. The power was disengagedwhen Vmax reached 80 Volts RMS or Impedance reached 200 ohms. An initialcycle was established with a one (1) second ramp to maximum powerfollowed by a two (2) second hold and then a one (1) second hold at aminimum power of 5 watts. If the power is left on too long, theadditional power applied to the vessel will rapidly increase theimpedance. In one embodiment it is envisioned that the power isdeactivated within 100 msec. Complete and translucent seals wereobtained at as low as 7 watts maximum power.

The time to Pmax for the series was 1 second. The observations were that5 W did not provide an adequate seal and both 10 W and 15 W began toshow charring of the vessel. It was found that translucency wasn'tnecessarily a good indication of a good seal. Burst tests of some clearseals did not achieve the desired 500 mm Hg (˜10 psi level). It wasfound that some charring of the seals seemed to produce stronger sealsthat reach a 500 mm Hg burst strength. A series of 30 tests were thenrun where the time to Pmax was reduced to 0.5 seconds in order to reducethe total time of the seal and to get more energy into the vessel morequickly.

The time to Pmax was fixed at 0.5 seconds and the time to Pmin was fixedat 0.2 seconds. Pmax and Pmin were then incrementally adjusted tooptimize the seal results. This testing established Pmax at 12 W andPmin at 5 W, with Pmin being as low as 0 Watts as providing reasonableand consistent seals. Subsequent testing attempted to bracket the rangefor which good seals could be achieved. This ranged from 10 W to 14 W.In other embodiments the range for Pmax and Pmin is between 5W to 10 W,alternatively between 2 W to 15 W.

In a second example, the goal was to enable seal times under 3 seconds.In this embodiment, power delivery of 12 watts for 1.1 seconds followed,by 5 watts for 1.5 seconds gave good results. These settings wereinitially set based on observations that seals at 7 W took about 3seconds. If shorter sealing times were desired, it was understood that ahigher power setting would be required since the seals are the result ofthe total energy delivered to the vessel.

Approximately 100 seals (See Table 1) were performed with varyingresults. The primary problem with obtaining repeatable seals at aconstant power setting was that there was often arcing between the jawsand a subsequent burn-through of the vessel. In particular, testsperformed using the parameters that worked on large vessels when appliedto smaller vessels often had arcing at the end of the seal cycle.Experimentation realized that settings were not simply power and timedependent. Further testing incorporated the impedance threshold andvoltage and current limits described below.

In another example seals were effected based on real-time measurementsof the impedance. Examples of viable seals were created at 7 W peakpower for 2.9 sec followed by 2 W of sustained minimum power. FIGS. 10and 11 show the power output on an oscilloscope for these seals. Themaximum output scale for the impedance on the user interface is 200ohms. When the impedance reaches 200 ohms, the programmed input powercurve switches to the next phase of the profile.

During the seals shown in FIG. 10, the maximum impedance was set to 175ohms. This seal was following the typical bathtub shaped curve ofimpedance changes. The tissue begins to desiccate and the impedancedrops. As it continues to dry out, the impedance begins a rapid rise. Inthis case, the impedance threshold was attained and the power was turnedoff.

Conclusions

Testing confirmed that controlled RF sealing of blood vessels can beachieved with as little as 7 Watts of power applied. Voltage and currentapplied during these seals were less than 50 volts and 0.6 A,respectively. The square area of the jaws used is 0.023 in²/14.84 mm².The maximum current density applied by the system and as represented byI/A=0.6 Amps/14.84 mm² or 0.040 A/mm².

These tests and examples demonstrated that vessels up to 6 mm in sizecan be sealed with a low power RF energy output that utilizes a smallbipolar grasper jaw end effector. Parameters of such a system includeapplied pressure, current density, low voltage, impedance monitor andmidpoint. Steps for sealing may include one or more of the following:

a. Apply pressure to the tissue sufficient to compress the instrumentjaws to less than or equal to 0.005″. This pressure must also be highenough so that as the tissue contracts during heating, the jaws do notdeflect and the gap between the jaws remains constant. Experimental dataindicates that this pressure requirement is between 65-110 lb/in². Inanother embodiment the pressure requirement may be up to approximately125 lb/in².

b. Radio frequency current is then applied to the tissue such that thecurrent density is in the range of 0.034-0.1 Amps/mm². This current issufficient to heat the tissue quickly so that the internal elasticlaminae will fuse. A temperature of about 140° C. is required for thisto occur.

c. Power delivery from the generator is generally less than 20 Watts todeliver this current density but may be as high as 35 Watts. Higherpower may shorten the sealing time.

d. After the tissue begins to desiccate, the power may be reduced by60-80% and heating is continued for a period of time before shuttingoff. The power can be reduced either when the tissue impedance reaches alevel of 150-250 ohms or at a set time interval.

e. The voltage of the system is limited to less than 100 Volts RMS andpeak voltage is typically in the range of 85 Volts RMS.

f. One or more wait states may also be interposed between the abovesteps.

As demonstrated, vessel sealing is possible using a low power system bylimiting jaw size and applying high pressure. A jaw of approximately 3mm in width and 10-12 mm in length with a cross-sectional area ofapproximately 15-22 mm² is preferred but other geometries arecontemplated. FIG. 9 shows one embodiment of an end effector jawgeometry, such as a Maryland style jaw, as used in connection withaspects of the present invention. When describing the surface area ofthe jaws in FIG. 9, reference is made to the surface area of the jawsthat actually align with each other and grasp around the tissue beingsealed. In some embodiments, there may be curved surfaces or taperededges to the jaw surface that does not actually perform the bulk of thesealing function. When describing jaw surface area, it is not intendedto encompass these portions of the jaw that are outside the normalboundaries of the sealing surface. In combination with the powerdelivery schemes described herein, the system results in a significantlyreduced power requirement over standard bipolar sealing systems. Powerrequirements in some embodiments are in the range of 10-35 Watts.

In accordance with other testing aspects, non-conductive spacers, suchas ceramic beads, were incorporated into the instruments to stop thejaws before they touch and prevent short circuits in the electricalsystems. The ceramic beads also provided a means of keeping the jawsparallel since the moving jaw will land on the top of the beads.

In the testing environment, a silk suture material (0.006″ diameter)that is non-conductive and will not melt during sealing was utilized tomaintain the separation between jaw surfaces and prevent arcing. In theexamples described in Table 1, two wraps of the suture were placedaround the upper jaw so that the jaws would be separated by 0.006″ whenthey were closed by the spring.

In accordance with another example, and with the non-conductive suturesin place, the power was set at 12 W as a nominal starting point andbracketed from 10 W to 14 W. When full jaw bites were sealed (100%filling of jaws with tissue), there were high quality seals, excellenttranslucency, with minimal sticking and charring. However, attempts toperform seals using these settings on smaller vessels that fill less(50-75%) of the jaw still resulted in arcing. Additional testingbracketed Pmax between 7 W and 15 W. Pmin was set at 5 W and bracketedbetween 4 W and 7 W. Since there was no control limit on parametersother than power and time, the lower power settings were used to producereasonable seals on smaller vessels in the range of 50-80% jaw tissuefill. When the vessels filled 100% of the jaws, the 7 W was notsufficient to seal and a higher power near 12 W was necessary toadequately seal these larger vessels.

In accordance with other examples, further seals were provided bysetting impedance thresholds in the user interface. It was then possibleto set break points in the power curve that could limit the powerdelivered to the jaws by watching the real-time rise in impedance.Additional seals were performed with power and time as the solemodifiers of the power curve. An impedance trigger point added to thesequence and control of power delivery enabled the generator to quicklyrespond to changes in impedance and make the necessary adjustments.

Current and Voltage Clamping

In another aspect of testing the device, current and voltage limits wereimplemented. Based on observation, by limiting the voltage to 100 Varcing was eliminated in vessels ranging from 2 to 7 mm in width. Theseparameters made it possible to seal vessels that filled any percentageof the jaws thus the process and device were not limited to fullyfilling the jaws with tissue material. As an experimental validation,raising the voltage limit to 150 volts again caused arcing. Thisconfirmed that the voltage limit is correctly stopping the arcing fromoccurring. The voltage maximum was set at between 75 and 100 volts forthe next series of seals performed.

As another method to determine a maximum current for sealing, a systemenergy check was performed to see what current level is required to boiloff saline that is placed between the jaws. It was found that 1.8 A wasneeded to cause the saline to begin to steam and boil away when RF poweris applied to the jaws and this was used as the maximum current forsealing.

In another example, it was determined that a fast application of energywith a high influx of current creates good seals. Examples includedfollowing the high current energy with a one (1) second burst of lowenergy with Pmin set at 5 W.

In another example, a set of jaws 0.409 inches in length were installedin the system. The old jaws were removed and found to have experiencedsignificant pitting due to the arcing incurred while there was novoltage limit in place. In addition to being longer than the originaljaws, the top edges of the jaws were eased to reduce any sharp cornereffects and high current concentrations that can occur with sharp edges.

In another example, seals were made with Vmax set to 75 volts and Imaxset to 1.8 A. There were never any incidents of arcing observed insubsequent seals. Seals were created with the following set ofparameters:

Pmax=15 W

Time at Pmax=2.5 sec

Pmin=5 W

Time at Pmin=1 sec

Vmax=75V

Imax=1.8 A

Time to Pmax=0.01

Time from Pmax to Pmin=0.01 sec

A series of thirty-two (32) seals were performed on two animals. Vesselsranged from 2 mm to 6 mm wide. Twenty (20) of the 32 seals from theseries were burst tested. All seals successfully withstood a minimum of360 mm Hg. Seals were also successfully performed on mesentery tissueusing the same settings.

FIGS. 10-14 show reproductions of oscilloscope traces captured for threedifferent seals demonstrating three different sizes of vessels. All weresealed using the above settings. All were set with the impedancethreshold at 200 ohms. Seal time was determined by observing when thepower was triggered to switch off. FIG. 11 shows the results for a 3.5mm Vessel with a 1.5 second seal time. FIG. 12 shows the results for a 5mm vessel with a 2.3 second seal time. FIG. 13 shows the results for a1.5 mm Vessel with a 0.75 second seal time.

FIG. 14 shows a reproduction of an oscilloscope trace captured foradditional sealing example where the maximum impedance was set to 175ohms. This impedance of the seal followed the typical curve of impedancechanges. Through the sealing process, the tissue begins to desiccate andthe impedance drops. As it continues to dry out, the impedance begins arapid rise. In this case, the impedance threshold was attained and thePmax was switched to Pmin for the duration of the run.

Those skilled in the art can readily recognize that numerous variationsand substitutions may be made in the invention, its use and itsconfiguration to achieve substantially the same results as achieved bythe embodiments described herein. Accordingly, there is no intention tolimit the invention to the disclosed exemplary forms. Many variations,modifications and alternative constructions fall within the scope andspirit of the disclosed invention as expressed in the claims.

What is claimed is:
 1. A surgical system for fusing tissue, the systemcomprising: an electrosurgical generator capable of deliveringelectrosurgical power; a surgical instrument electrically connected tothe electrosurgical generator and adapted to transfer electrosurgicalpower from the electrosurgical generator to a distal end of the surgicalinstrument; and a power control circuit for controlling the delivery ofradio frequency energy to tissue in contact with the distal end of thesurgical instrument; wherein the surgical system is configured to:deliver radio frequency energy at a non-pulsing power to the tissue fora period of time of 3 seconds or less, the non-pulsing power having noless than 7 Watts and no more than 35 Watts, the non-pulsing powerfurther causing the tissue to begin to desiccate and to fuse within theperiod of time.
 2. The surgical system of claim 1, wherein the radiofrequency energy-is delivered to the tissue with a current density below0.12 Amps per square millimeter.
 3. The surgical system of claim 1,wherein the surgical system is configured to: calculate an impedance ofthe tissue being fused; and limit the flow of non-pulsing power when theimpedance of the tissue being fused reaches a set impedance thresholdwithin the period of time.
 4. The surgical system of claim 1, whereinthe surgical system is configured to: calculate an impedance of thetissue being fused during the period of time; and terminate the flow ofnon-pulsing power when the impedance of the tissue being fused reaches apredetermined level.
 5. The surgical system of claim 1, wherein thedistal end of the surgical instrument has a pair of end effectors, eachend effector having a contacting surface area of less than 22 squaremillimeters.
 6. The surgical system of claim 6, wherein each of the endeffectors has a contacting surface area of between 15 and 22 squaremillimeters.
 7. The surgical system of claim 1, wherein the non-pulsingpower has an output current of-between 0.2 and 1.75 Amperes RMS.
 8. Thesurgical system of claim 1, wherein the non-pulsing power has an outputcurrent of-between 0.75 and 1.00 Amperes RMS.
 9. The surgical system ofclaim 1, wherein the non-pulsing power has an output voltage of between5 and 135 Volts RMS.
 10. The surgical system of claim 1, wherein thenon-pulsing power has an output voltage of between 70 and 90 Volts RMS.11. The surgical system of claim 1, wherein the distal end of thesurgical instrument has a pair of end effectors adapted to apply between25 and 125 lb/in² of pressure to the tissue being fused.
 12. Thesurgical system of claim 1, wherein the non-pulsing power further causesthe tissue to fuse to successfully withstand a burst test of 360 mm Hgor more.
 13. A power control system for delivering radio frequencyenergy to a surgical instrument, the power control system comprising: apower supply for delivering an output voltage and an output current to adistal end of the surgical instrument; a sensing circuit for detectingparameters indicative of an impedance of a tissue portion being fused; apower sequencing module for automatically sequencing an electrosurgicalpower delivered to the surgical instrument; wherein the power sequencingmodule is adapted to: apply non-pulsing power of no less than 7 Wattsand no more than 35 Watts to the tissue portion for a period of time of3 seconds or less, wherein the period of time is measured from thebeginning of the application of the non-pulsing power and continuesthrough the beginning of a desiccation of the tissue portion and througha drying out and the fusing of the tissue portion.
 14. The power controlsystem of claim 13, wherein the power sequencing module is adapted toterminate the flow of power to the tissue being fused when the impedanceof the tissue being fused reaches 150 or more ohms.
 15. The powercontrol system of claim 13, wherein the power sequencing module isfurther adapted to calculate an impedance of the tissue being fusedthrough the impedance sensing circuit during the period of time; andlimit the flow of power to the tissue being fused by between 60 and 80%when the impedance of the tissue being fused reaches a set impedancethreshold within the period of time.
 16. The power control system ofclaim 13, wherein the power sequencing module is further adapted todeliver the reduced power to the tissue being fused for a predeterminedlength of time prior to terminating the flow of power to the tissuebeing fused.
 17. The power control system of claim 13, wherein the powersequencing module is further adapted to calculate an impedance of thetissue being fused through the sensing circuit during the period oftime; and terminate the flow of power to the tissue being fused when theimpedance of the tissue being fused reaches a predetermined level. 18.The power control system of claim 13, wherein the non-pulsing power hasan output voltage, and the power sequencing module is further adaptedto: hold the non-pulsing power to 35 Watts; and limit the output voltageto a maximum of between 70 and 85 Volts.
 19. The surgical system ofclaim 13, wherein the power sequencing module is adapted to fuse thetissue to successfully withstand a burst test of 360 mm Hg or more. 20.A surgical system for fusing tissue, the system comprising: anelectrosurgical generator capable of delivering electrosurgical power; asurgical instrument electrically connected to the electrosurgicalgenerator and adapted to transfer electrosurgical power from theelectrosurgical generator to a distal end of the surgical instrument;and a power control circuit for controlling the delivery of radiofrequency energy to the tissue through the distal end of the surgicalinstrument; wherein the surgical system is configured to deliver a radiofrequency energy to the tissue, the radio frequency energy having anon-pulsed power having an output current and an output voltage; andapply the non-pulsed power to the tissue for a period of time while thenon-pulsed power is held at between 7 Watts and 35 Watts, while allowingthe output current and the output voltage to fluctuate, wherein theperiod of time is measured from the beginning of the application of thenon-pulsed power and continues through fusing of the tissue, and thenon-pulsed power causes the tissue to begin to desiccate within theperiod of time, wherein the period of time is 3 seconds or less.
 21. Thesurgical system of claim 20, wherein the surgical instrument has a pairof end effectors, each end effector having a contacting surface area ofless than 22 square millimeters.
 22. The surgical system of claim 20,wherein the surgical system is configured to: calculate an impedance ofthe tissue being fused; limit the flow of non-pulsed power when theimpedance of the tissue being fused reaches a set impedance threshold;and terminate the flow of non-pulsed power when the impedance of thetissue being fused reaches a predetermined level indicative that thetissue being fused is desiccated.
 23. The surgical system of claim 20,wherein the surgical system is configured to: limit the output voltageto a maximum of between 70 and 85 Volts.
 24. The surgical system ofclaim 20, wherein the surgical system is configured to apply thenon-pulsed power to fuse the tissue to successfully withstand a bursttest of 360 mm Hg or more.
 25. A method of fusing tissue, the methodcomprising: providing a surgical system having an electrosurgicalgenerator and a surgical instrument surgical instrument electricallyconnected to the electrosurgical generator and adapted to transferelectrosurgical power from the electrosurgical generator to a distal endof the surgical instrument; delivering a radio frequency energy to thetissue, the radio frequency energy having a non-pulsed power having anoutput current and an output voltage; and applying the non-pulsed powerto the tissue for a period of time while the non-pulsed power is held atbetween 7 Watts and 35 Watts, while allowing the output current and theoutput voltage to fluctuate, wherein the period of time is measured fromthe beginning of the application of the non-pulsed power and continuesthrough fusing of the tissue, and the non-pulsed power causes the tissueto begin to desiccate within the period of time, wherein the period oftime is 3 seconds or less.
 26. The method of claim 25, furthercomprising: limiting the output voltage to a maximum of between 70 and85 Volts.
 27. The method of claim 25, further comprising: fusing thetissue to successfully withstand a burst test of 360 mm Hg or more. 28.The method of claim 25, further comprising: terminating the flow ofpower to the tissue being fused when the impedance of the tissue beingfused reaches 150 or more ohms.
 29. The method of claim 25, furthercomprising: terminating the flow of non-pulsed power when the impedanceof the tissue being fused reaches a predetermined level indicative thatthe tissue being fused is desiccated.
 30. The method of claim 25,further comprising at least one of: applying pressure to the tissuesufficient to compress the tissue to less than or equal to 0.127millimeters; or applying pressure of between 65 and 110 lb/in² tocompress the tissue between a pair of end effectors on the surgicalinstrument.